Substrate mapping (or wafer mapping) is a process in which the performance of semiconductor devices on a substrate is represented by a map showing the performance as a colour-coded grid. The map is a convenient representation of the variation in performance across the substrate, since the distribution of those variations may be a clue as to their cause.
Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications.
The concept also includes the package of data generated by modern wafer testing equipment which can be transmitted to equipment used for subsequent 'back-end' manufacturing operations.
Wafer testing is a step performed during semiconductor device fabrication. During this step, performed before a wafer is sent to die preparation, all individual integrated circuits that are present on the wafer are tested for functional defects by applying special test patterns to them. The wafer testing is performed by a piece of test equipment called a wafer prober. The process of wafer testing can be referred to in several ways: Wafer Final Test (WFT), Electronic Die Sort (EDS) and Circuit Probe (CP) are probably the most common.
History
A wafer map: different bins are represented by different coloursA strip map: this strip map represents five panels on one strip. The lowerleft square around the die on each panel represents a reference die, which is used to align between wafer testing and die attachment
The initial process supported by substrate maps was inkless binning.
Each tested die is assigned a bin value, depending on the result of the test. For example, a pass die is assigned a bin value of 1 for a good bin, bin 10 for an open circuit, and bin 11 for a short circuit. In the very early days of wafer test, the dies were put in different bins or buckets, depending on the test results.
Physical binning may no longer be used, but the analogy is still good. The next step in the process was to mark the failing dies with ink, so that during assembly only uninked dies were used for die attachment and final assembly. The inking step may be skipped if the assembly equipment is able to access the information in the maps generated by the test equipment.
A wafer map is where the substrate map applies to an entire wafer, while a substrate map is mapping in other areas of the semiconductors process including frames, trays and strips.
A wafer, also called a slice or substrate, is a thin slice of semiconductor material, such as a crystalline silicon, used in electronics for the fabrication of integrated circuits and in photovoltaics for conventional, wafer-based solar cells. The wafer serves as the substrate for microelectronic devices built in and over the wafer and undergoes many microfabrication process steps such as doping or ion implantation, etching, deposition of various materials, and photolithographic patterning. Finally, the individual microcircuits are separated (dicing) and packaged.
E142
As with many items in the Semiconductor process area, also for this process step there are standards available. The latest and most potential standard is the E142 standard, provided by the SEMI organization. This standard has been approved via ballots for release in 2005.
It supports many possible substrate maps, including the ones named above. While the old standards could only support standard bin maps, representing bin information, this standard also support transfermaps, which can help in tracing back dies on strips to the locations they come from off the wafer for example.
External links
SEMI organization: organization which is working on semiconductor process standards.
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